Outflow physiology of the mouse eye: pressure dependence and washout.

PURPOSE: Mice are commonly used in glaucoma research, but relatively little is known about aqueous outflow dynamics in the species. To facilitate future use of the mouse as a model of aqueous humor outflow, several fundamental physiological parameters were measured in the mouse eye.
METHODS: Eyes from adult mice of either sex (C57BL/6 background) were enucleated, cannulated with a 33-gauge needle, and perfused at constant pressure while inflow was continuously measured.
RESULTS: At 8 mm Hg, total outflow facility (C(total)) was 0.022 ± 0.005 μL/min/mm Hg (all values mean ± SD; n = 21). The flow-pressure relationship was linear up to 35 mm Hg. The conventional outflow facility (C(conv)) was 0.0066 ± 0.0009 μL/min/mm Hg, and the unconventional outflow (F(u)) was 0.114 ± 0.019 μL/min, both measured at room temperature. At 8 mm Hg, 66% of the outflow was via the unconventional pathway. In a more than 2-hour-long perfusion at 8 mm Hg, the rate of facility change was 2.4% ± 5.4% (n = 11) of starting facility per hour. The ocular compliance (0.086 ± 0.017 μL/mm Hg; n = 5) was comparable to the compliance of the perfusion system (0.100 ± 0.004 μL/mm Hg).
CONCLUSIONS: Mouse eyes are similar to human eyes, in that they have no detectable washout rate and a linear pressure-flow relationship over a broad range of intraocular pressures. Because of the absence of washout and the apparent presence of a true Schlemm's canal, the mouse is a useful model for studying the physiology of the inner wall of Schlemm's canal and the conventional outflow tissues.